AOAC Official Method 936.18 Theobromine in Theobromine–Calcium Salicylate Drugs
First Action 1936
Final Action
A. Method I
Dry ca 0.5 g test sample at 110°Cto constant weight. Weigh 0.2 g test portion into glass-stoppered 100 mL volumetric flask, add 2 mL CH3COOH, and warm on steam bath. Add 10 mL boiling H2O and shake until dissolved, adding more boiling H2O if necessary. Cool solution to room temperature. (Solution should be clear or nearly so.) Add 50 mL 0.1M I2, 939.13 (see A.1.07), 20 mL saturated NaCl solution, and 2 mL HCl. Shake well and dilute to volume with H2O. Shake again and let stand overnight. Filter, discarding first 10 mL filtrate. Titrate 50 mL filtrate with 0.1M Na2S2O3, 942.27 (see
A.1.13), using starch solution, as indicator (mix ca 2 g finely powdered potato starch with cold H2O to thin paste; add ca 200 mL boiling H2O, stirring constantly, and immediately discontinue heating. Refrigerate. Prepare fresh weekly). 1 mL 0.1M I2 = 0.00450 g theobromine, C7H8O2N4.
